Electrical fuse and method



EXAMINE CROSS REFgNCE Mam?? Feb. 19 1924.

H. E. TRENT ELECTRICAL FUSE AND IETHOD Filed July 10, 1918- Patented Feb. 19, 1924.

HAROLD E. TRENT, OF LAN'SDOWNE, PENNSYLVANIA.

ELECTRICAL EUsE AND METHOD.

I Application led J'uiy 10, 1918. Serial No. 244,243.

To all whom z't may concern:

Be it known that I, HAROLD E. TRENT, a subject of the King of Great Britain, residing at 210 N. Lansdowne Av., Lansdowne,

in the county of Delaware and State of Pennsylvania, have invented a certain new and useful Electrical Fuse and Method, of which the following is a specification.

My invention relates to electric fuses capable of use either in cartridges or other enclosures with or without a filler.

The main purpose of my invention is to delay the fusion and prevent or delay vaporization of a portion of a fuse when large 5 currents pass through it, so as not to have the melting or vaporization of the metal occur all at the same time, and t0 reduce the extent of explosion from the vaporization of the remainder of the fuse by cushioning 0 it, and prevent damage or carbonization of the tube or other containers.

A further purpose is to reduce the total mass of the fuse to a minimum, reducing alike the weight, cost and total explosive 5 effect of the fuse.

A further purpose is to retard vaporization of any desired portion of a conductor by adding to it a heat conducting mass, increasing alike the mass within which the heat is distributed and the surface for conduction to the air and for radiation.

A further purpose is to supply fuses with a coating, preferably an electrical insulator, which shall both retard the time and cushion `5 lthe explosive force of vaporization.

Further purposes will appear in the specification.

I have preferred to illustrate m invention by a few only of the many orms in which it may appear, selecting some which are practical, eicient and inexpensive and which at the same time will illustrate the principles of my invention.

Figure l is a side elevation, partly sectioned, of an enclosed cartridge fuse embodying my invention.

Figure 2 is an edge view of an open link fuse.

Figure 3 is a side elevation partly broken away of a form having a number of fuse elements in parallel..

t Figure 4 is a section of Figure 3 upon lines IV-IV.

Flgure 5 is a top plan view of a modified form of fuse link.

Figure 6 is a side elevation, partly sectioned, of a modified form.

Figures 7 and 8 are longitudinal, sections of enclosed links showing modified forms.

Flgure 9 is a side elevation partly broken away showing one of my fuses in an enclosing tube.

In the drawings similar numerals indicate like parts.

Where fuses may be subjected to an excess of current through the fuse a number of different conditions may arise, depending upon the extent of the excess.

With a small continued excess any character of fuse will melt and open the circuit. Where the excess is not very great the fusion or even vaporization can readily be limited to a' part only of the fuse by such expedients as reducing the current-carrying cross section. Various means for limiting the extent of fusion or vaporization have been provided, some intended for open fuse links primarily, some for enclosed fuses and others applicable to either.

One of the earliest of these, shown in both open and enclosed fuse uses and having spaced points of restricted section (fusing points) to drop out an intermediate portion both in the open and enclosed forms, is seen in German Patent No. 121,- 217 to Siemens & Halske, Actien-Gesellschaft in Berlin, dated February 27, 1900.

Another, showing spaced restricted cross sections for the same purpose in an enclosed fuse only, appears in United States patent to Yates, No. 1,028,173 of June 4, 1912.

A third, in which the fuse wire is electroplated with electrically conducting material (copper) at an intermediate point to decrease its electrical resistance there and strengthen it, is described in British patent to Rawlings and Smith No. 27,401 of 1907. This provides spaced points of smaller section and hi her resistance and recognizes the applicability of the invention to both enclosed and open fuseaff All of these and others are effective if the Y (iig overload be not too great to divide the voltage between the several points of rup ture and to reduce the total metal melted or vaporized by dropping out the intermediate fuse section, without fusing it, whether the metal at the point of rupture be melted merely or vaporized.

However, with extreme overloads the entire fuse is vaporized. As this may happen to most fuses through accidental connection with other circuits, or by reason of abnormal conditions in its own circuit, my invention is primarily directed to protection against injury in such a case at the same time that the fuse is capable of performing the functions on lower overloads which the fuses of the patents named perform.

Since I contemplate protection from injury Where the entire fuse vaporizes, in the case of every fuse put out, my irst concern is to reduce the total quantity of fuse material to a minimum; my second, to cushion the effect of the explosion; my third, to distribute the stresses due to the explosion; and my fourth, to delay the vaporization of a part of the fuse in order to avoid having all of the explosion at the same time. All of these advantages are readily attained in a single structure.

The character of cross section of fuse to which my invention is a plied is not material. lt may be round, at or of any other preferred shape. From the standpoint of uiring and using a minimum of fuse material aud having to deal with a minimum of vapor from explosion I much prefer that the fuse be of uniform cross section throughout, but other features of my invention are advantageous even when applied to fuses havin restricted cross section at the point or points of intended rupture and such a form is illustrated herein.

Taking up the drawings z--In Figure 1, I have shown a cartridge fuse whose fusible conductor 1 is preferabl lead or zin-c, shown as of flat metal prefere ly of the same material and density of uniform cross section and electrical conductivity throughout. It is removable and is secured to internal fuse terminals 2, within a cartridge 3. This comprises a fiber casing or tube 4, caps 5 and knife blade outer terminals 6, by which the entire fuse may be inserted between terminals. The fuse element may be made removable (the cartridge reillable) or not as preferred.

The fuse is partly covered by a heat-conducting coating which not only reduces the temperature to which the combined section and coating will be raised by the same number of heat units generated by the current in that part of the fuse but supplies a much larger surface for distributing the heat to the air and tube interior by convection and radiation..

The coverin is applied to a section or sections only of t e fuse, as at 7, 8 and 9, leaving one or more intermediate sections, as 10 and 11, which will heat more rapidly than the covered sections because their heatreceiving mass and heat-distributin surfaces are both smaller, per unit lengt By making the coverings 7, 8 and 9 of heat conductors which are at the same time at least oor conductors of electricity and, preferab y, electrical non-conductors, I am able to keep down the total volume of volatilizable material to a minimum. I thus obtain all of the benefit of the heat conductivity of the coverings without the objectionable increase of vapor which the use of an electrically conducting cover would entail. I also reduce the weight and cost as compared with an electrically conducting cover of corresponding heat-distributing value, even if it were practicably possible to prevent the vaporization of such a cover- In addition to the advantages of heat conductivity without danger of vaporization, I secure still other advantages from my covering'by making it of a firm (preferably molded) cushionin.Y material which delays and subsequently t ics up the explosive force due to vaporization. That due to the volatilization of the parts outside of the covering is taken up upon the outside and that due to the fuse length within the covering is received upon the interior surface of the covering.

On the less extreme overloads, the additional heat-receiving mass ofthe coating and its greater surface for heat conduction to the air and convection through it and for radiation delay or prevent. fusion of the part within the coating while the exposed part or parts are fusing and interru ting the circuit. Where there' are severa exosed parts this results in dropping out the intermediate section or sections as in the case of the structures described in the patents hereinbefore mentioned.

Where the fusion of the covered sections is merely delayed until after fusion of the exposed section or sections, there is an intermediate extent of overload in which the exposed section or sections vaporize and the covered sections are merely fused.

There are probably a great many materials which areelectrical insulators or which have sufficiently poor electrical conductivity not toinclude any appreciable vaporizable content. so as to serve the purpose, and which are heat conductors and are suited to perform a cushioning function when the fuse is vaporized.

Without attempting to explore this field fullv. I consider it sufiicient for the purpose to disclose one good composition for this purpose. It is made up of asbestos liber,

manganese dioxide, felspar and plaster of Paris in equal proportions with suilicient silicate of soda to form part. There is an investment compound for dental use known as the Brophy Investment Compound upon the market, made by the Ransom and Randolph Company of Toledo, Ohio, which may be used instead of the plaster of Paris in the same proportion where it is desirable to give the composition greater irmness. Either of these compositions has the characteristics indicated and is suliiciently hard when molded to hold its'form mechanically and remain in place without a covering.

The function of the asbestos liber is to tie or bond the parts altogether, adding also to the resilience or cushioning capacity of the composition. The investment compound or plaster of Paris causes quick setting and contributes to the body and resilience of the composition. The manganese dioxide gives heat conductivity sufcient for the purpose without undesirably reducin the electrically insulating properties o the composition. The felspar tends to delay the setting of the composition and also gives body to it. The silicate of soda renders the composition pasty so that it can be molded suitably and also hardens the molded covering.

The various ingredients may be used or omitted or substitutes used for them as the functions performed by them are important, desirable or negligible in the use intended. The composition which is best for the purpose will vary somewhat with the' intended use and will be determined considerably by the preference of the designer. In view of the instruction given herein, alterations of the composition to obtain the characteristics of heat conductivity, freedom from objectionable vaporizable content and cushioning effect upon the vaporized material where vaporization is anticipated may readily be Secured by experimentation wlth a variety of quite different ingredients. For this reason I contemplate including in my claims an materials or combination of materials whic may be substituted for the composition described by me.

In Figure 2 I show a fuse which may be used as an open fuse as indicated or may comprise the removable fuse element for a cartridge construction. In it the fuse 12 is coated as at 13, 14 and 15 with a composition embodying my invention leaving intermediate bare spaces 16 and 17 which will fuse or vaporize prior to the fusion or vaporization of the parts included within theA coatings because of the greater heat-receiving capacity and heat-radiating and conducting surfaces of the covered or coated sections.

In Figures 3 and 4 a fuse is shown which is made up of terminals`18 connected b a number of fuse elements 19 in parallel, al11 of the parallel elements being coated throughout portions of their lengths leaving intermediate spaces bare as shown.

The operation of this fuse will be the same as with those previously described, the fuse elements in parallel operating substantially the same as individual fuses.

It will be noted in Figure 4 that the individual fuse elements are square in cross section instead of flattened as in Figures 1 and 2. Obviously in all of my forms the fuse could be made of round or flat section or of any other shape preferred.

Though my invention is applicable to a fuse of uniform cross section, material and density, it ma be applied also to increase the effect of a filse havlng spaced constricted cross sections or otherwise reduced conductivity, adding the advantage of my invention to whatever advantage the particular difference in material, density or section of the fuse itself may present; and I have shown such a construction in Figure 5. Here the fuse, having terminals 20, is shown as of reduced cross section and also as bare at the sections 21; Whereas the intermediate sections are enclosed within coatings or coverings 22 embodying my invention, so as to increase the susceptibility of the fuse to time variation in the fusin or vaporizing ofthe parts by changing the eat capacity and heat radiating and conducting surfaces.

In Figure 6 I have shown the application of my fuse to a transformer fuse-holder 23. It comprises a receptacle 24, a removable core 25 and ausible conductor 26 having alternating portions coated or covered with an insulating compound embodying my invention and serving to distribute the heat and conduct it away from the enclosed fuse portions. The intermediate sections are bare and the operation is the same as in the previous forms.

In Figure 7 the fusible conductor 27 is removable and extends from a terminal 28 at one end of a tube 4 to a spring 30 which is connected with a contact 31 at the other end. The coverings are shown at 29. The caps 5 are removable to replace the fuse. The operation of the invention is the same here as in the other figures but the contacts at the ends of the cartridge are made by clips engaging the caps 5.

In Fi ure 8 I have shown the cartridge tube 4:2 having caps 52 at the ends thereof, riveted to parts of split clamps 33, 33. The clamps are tightened upon a removable fuse 1 by a screw 34.

In this case the insulating material 35 forms a-tube or covering about a considerable length of the fuse, with air spaces at intervals therein, having the same eiiect as the bare spaces in the other forms except that vaporization of tho/tube in these au:

s aces drives the vapor against the enc osing wall of composition, giving a greater benefit from the cushioning effect of the composition during the explosion of these bare sections of the fuse.

The various forms of fuses shown, as well as many other forms, embodying my invention may be protected against mechanical injury and moisture before use and also may be made to perform an additional function when in position, by the use of a covering tube of special value as a shipping tube and during storage or handling of electrically insulating material such as shown at 37, protecting the coverings 36, in Figure 9. The tube is here shown as terminating at a point short of the end of the fuse so as to permit the fuse to be inserted in place without removal of the tube. Good materials for the construction of the tube would be asbestos or any other insulatin fibrous material such as paper coated witi shellac.

In use the tube restricts the explosion of the vaporized metals and is advantageous whether the fuse be otherwise enclosed or DC'.

It will be noted that in all the forms described there are the same characteristics of heat conductivity and substantial absence of vaporizable content in the covering. Though this is beneficial in itself without the cushioning effect of the composition and the cushioning effect is also separately beneficial and is believed to be new by me in so far as it is'molded upon and furnished thus with the fuse itself, the combination of the two is most highly effective.

It will be noted that my use the smallest quantity of referred forms sible or vaporizable metal that will carry the current,4

carry their own cushioning and heatdistributing provisions, can be split up mto sections to divide the voltage just as in the -patents noted, and can be protected against mechanical injury and moisture by means which need not be distributed when the fuse is a plied.

avin thus described my invention, what I c aim as new and desire to secure by Lett-ers Patent is:

1. A fuse comprising a fusible conductor, in combination with a firm covering cohesive upon the conductor, of cushioning Amaterial at separated intervals adapted to absorb the explosive forceof the vapor of the metal of the fusible conductor, in case of vaporization of the same and ashipping tube enclosing and supporting these coverings.

2. .An electrical conductor of uniform cross section, in combination with a cushioning covering for separated portions of the length of said conductor between the terminals supported thereon by its own cohesion, the remainder of the conductor being exposed and a shipping tube enclosmg and supporting these coverings.

3. An enclosing casing and terminals therein, in combination with a renewable fuse therefor, comprising a fusible conductor having a plurality of e osed sections and a plurality of intermedlate coverings mounte and supported thereon by reason of their own coheslon, composed of cushioning material.

4. An electrical conductor of uniform cross section, in combination with a cushioning covering for a portion of the length of sald conductor supported thereon by its own cohesion, the remainder of the conductor being exposed, and a mechanically-su porting shipping tube retaining said con uctor in alifrnment.

5. n electrically-conducting fuse strip in combination with a covering therefor comprising a substantially non-conductor of heat mixed with a heat conductor to form a cohesive covering substantially a non-conductor of electricity and having low heat conductivity.

HAROLD E. TRENT. 

